Addition of Shipping Services, Economy, Plus & Premium.

 As per http://www.shipwire.com/w/developers/xml-shipping-rate-api-faq/
Added a check to make sure post object is set before trying to access it
Update whitespace & braces to WP Coding Standards

Just a bit of nit-picking related to WP coding standards. No
functionality has changed.
Use get_the_terms() instead of wp_get_object_terms() when duplicating products.

Issue #100.
Replace almost all wp_get_object_terms() with wpsc_get_product_terms().

The only exceptions are calls to wp_get_object_terms() with multiple $ids as
arguments.

Issue #100.
Fix fatal error on front end.